With the features of being thin and capable of consuming less electric power, liquid crystal display devices have a wide variety of applications ranging from large-sized displays to portable information terminals, and thus development of the liquid crystal display devices is inactive progress. In regard to liquid crystal display devices developed thus far, multiplex drive for the TN mode and STN, active matrix drive using a thin film transistor (TFT) for TN, and the like have been developed and put to practical use. However, since these drive modes use nematic liquid crystals, the response speeds of the liquid crystal materials are as slow as several milliseconds (ms) to several ten milliseconds (ms), and it cannot be said that the liquid crystal materials are sufficiently capable of coping with moving video image displays.
Ferroelectric liquid crystals are liquid crystals which have response speeds that are very short in the order of microseconds (μs), and are appropriate for high speed devices. Since ferroelectric liquid crystals have superiority such as wide viewing angles, it is expected that high performance liquid crystal display devices can be provided.
Since ferroelectric liquid crystals have high birefringence, in a liquid crystal display device which uses a ferroelectric liquid crystal, in order to suppress the occurrence of color shift and thereby obtain a satisfactory white display, it is necessary to make the cell gap very narrow to less than 2 μm. However, with a narrow cell gap, there is a problem that due to the occurrence of thickness unevenness, and to the occurrence of color unevenness or display unevenness caused by thickness unevenness, the yield in production is decreased.
Thus, a ferroelectric liquid crystal which can realize satisfactory white display even in a liquid crystal display device having a large cell gap is desired.
For the purpose of providing a liquid crystal display device which enables a black-and-white display with high visibility by preventing coloration caused by a birefringence effect, for example, Patent Document 1 suggests that a substrate is made to exhibit birefringence, and also, the principal optical axis of the substrate is disposed to be slanting by 30° from the normal line of the smectic layer of the ferroelectric liquid crystal, to thereby adjust the difference in retardation of the substrate and the liquid crystal layer to a predetermined range.
Furthermore, although not related to ferroelectric liquid crystals, in regard to nematic liquid crystals, it is known to add a liquid crystal material in order to improve display characteristics. For example, Patent Document 2 suggests adding a liquid crystal material having a desired birefringence or a liquid crystal material having a relatively high birefringence.
Furthermore, in Patent Document 3, although not related to ferroelectric liquid crystals, in regard to nematic liquid crystals, a tetracyclic ester compound and an ether compound, both of which have a predetermined structure having a benzene ring and three cyclohexane rings in total introduced into the main chain, are disclosed for the purpose of providing a liquid crystalline compound which is suitable for super-twist displays.